This invention relates to a camshaft construction for the engine of an outboard motor and more particularly to a non-metallic camshaft for a four-cycle, outboard motor engine.
Two-cycle internal combustion engines have been frequently used as the prime mover for an outboard motor. The reason for the use of two-cycle engines is because of their compact nature and their high specific output. These features are particularly important in an outboard motor due to the very compact nature of such a propulsion device.
However, with increasing concerns about environmental protection, there has been a growing interest in the application of four-cycle engines for many applications that previously utilized two-cycle engines because of their aforenoted advantages. One of the advantages of four-cycle engines over two-cycle engines is also a feature that gives some disadvantages in connection with outboard motor application.
With two-cycle engines, the lubricating oil for the engine is generally consumed during engine running. That is, although two-cycle engines may use direct lubricating systems, the oil used for lubrication nevertheless is consumed during engine operation and any residual amounts is discharged to the atmosphere. This obviously has some environmental problems.
Four-cycle engines, however, have greater complexity than two-cycle engines, and thus tend to be more expensive. Furthermore, the greater number of moving parts also gives rise to concerns of potential wear and service requirements.
One area where such additional components are required and where the components are subject to wear is the valve actuating mechanism for the engine. Unlike two-cycle engines, four-cycle engines generally have poppet-type valves that are operated through an operating mechanism that includes a camshaft. The camshaft either operates the valves directly or through intermediaries, such as push-rods or the like. In any event, the cam lobes are subject to wear.
In addition, the camshaft is driven by a timing drive at one-half crankshaft speed, and this requires the provision of some form of timing gear or sprocket on the camshaft. Furthermore, at times the camshaft may be utilized to operate other mechanisms, such as operating the plunger of a fuel pump. Thus, it has been the practice to employ hardened steel shafts for this purpose, and these not only add to the cost, but require high-cost components that are engaged by the camshaft so as to avoid their wear also.
It is, therefore, a principal object of this invention to provide an improved, low-cost, long-life camshaft for a four-cycle engine.
It is a further object of this invention to provide an engine design that accommodates the use of a nonmetallic camshaft that can be formed from a resinous plastic or the like.